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6.9 Overheating

Started by ramiro, 26 July 2022, 10:20 AM

ramiro

Hello,
Is a 6.9 supposed to run over 100C when you drive it over 180 KMH for a while when the outside temperature is around 30C ?
I changed the Thermostat, Water pump , flushed the System multiple Times and recored the Radiator 2 times (1. standart core , 2.Perfomance core) but it didn't change anything .
Yesterday we had 35 and the Temp was always a little below 100C while drive slower then 120KM with air condition on.

The Radiator also had 100 C and ~ 85 on the Outlet so the coolant is flowing.

Today i checked the Headgasket with a cheap tester that changes color and it changes from blue to green , but i don't have any cooland loss , white smoke , or water in the oil.

Should a 6.9 under all cirumstances run below 100C ?

As is see everything speaks for a broken headgasket but i don't want to tear the engine apart and find out it wasn't the headgasket.

Greeting from germany
Ramiro



raueda1

Quote from: ramiro on 26 July 2022, 10:20 AMHello,
Is a 6.9 supposed to run over 100C when you drive it over 180 KMH for a while when the outside temperature is around 30C ?
I changed the Thermostat, Water pump , flushed the System multiple Times and recored the Radiator 2 times (1. standart core , 2.Perfomance core) but it didn't change anything .
Yesterday we had 35 and the Temp was always a little below 100C while drive slower then 120KM with air condition on.

The Radiator also had 100 C and ~ 85 on the Outlet so the coolant is flowing.

Today i checked the Headgasket with a cheap tester that changes color and it changes from blue to green , but i don't have any cooland loss , white smoke , or water in the oil.

Should a 6.9 under all cirumstances run below 100C ?

As is see everything speaks for a broken headgasket but i don't want to tear the engine apart and find out it wasn't the headgasket.

Greeting from germany
Ramiro

I'm going to say "NO."  Something is wrong, as you already suspect. My car had similar issues as yours, though maybe not quite as bad.  As a reference, mine now runs in very low 90deg range with A/C on at similar speeds and 44deg outside (yes, that's hot!  Summer in Las Vegas).  No problems at all.

It was not always this way.  I replaced thermostat and all hoses, flushed the block and had radiator flushed and descaled and flow tested.  Problem gone.  The radiator shop said flow was about 30% blocked with scale, kalk etc.  For other I reasons I had the whole engine apart at the time.  There was no visible scale build-up in the block.  I had the heads had been boiled out too, so none of the coolant passages had any scale buildup either.  So, after all that, I think my car is probably close to the ideal case.

In your case I don't see obvious head gasket issues.  More likely, I think, is an obstruction someplace in the engine itself.  I'm confident that substantial scale build-up could easily restrict flow enough to cause your problems.  At 180kph and 43deg I'd guess I've driven close to the design limit and never over 100deg.  Also, what does the temp do at low speeds and moderate temperatures?  In any case, I'm not sure how you deal with severe scale in the block or heads.  Obviously you could tear it apart and boil block and heads but that's an extreme measure.  Can motor flushes achieve that same thing?  I really don't know.  Hopefully somebody else will comment.  One thing you could to try is turning the heater on and seeing what happens.  That won't be a fun test when it's 40deg outside.  Keep us posted.  Good luck and cheers,
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

ramiro

44C and under 100 would be unbelievable for me , yesterday i had 98 also at low speed and idle when we had 35.
Do you have the euro radiator or the bigger us version without oil radiator ?

It also takes forever to go down to ~90 with slow driving when it reached ~115.

Blocked blocked would it not mean that the heat would not get transfered to the coolant and the engine would get hot in some places without the cooland overheating ,and if the coolant gets to hot the problem should be outside the engine or the engine makes too much heat?

I flushed the system with Acid several times over 2 years , and the coolant stays somewhat clear now and there are no rust pieces coming out, the radiator is also freshly recored so it should be clean.

Heater makes no real difference atleast at idle when i tried.


rumb

Dont forget the fan clutch. Remember that it is specific to the 6.9.

I assume the electric fan is working correctly. A quick hack to to add a 1.4K ohm resistor to the temp sensor to make the fan turn on sooner.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

ramiro

The Fan turns off over ~3000 RPM so at 180 it should not make any difference and under 3000 i can clearly hear it.

The Electrif fan also works fine but does not really make a difference i installed the bigger on from a w126.

raueda1

Quote from: rumb on 26 July 2022, 01:17 PMDont forget the fan clutch. Remember that it is specific to the 6.9.

I assume the electric fan is working correctly. A quick hack to to add a 1.4K ohm resistor to the temp sensor to make the fan turn on sooner.
Thanks Robert, yes, I also changed clutch.  My clutch was totally blown.

Ramiro:
My car is unmodified euro version.  The radiator has transmission cooler only.  Back to the problem.  I think at this point I'd use an IR heat gun to carefully map the temperature of the engine to the extent possible. Why not?  But honestly, I doubt that there would be substantial differences because the thermal conductivity of the engine is very high, so a small hot spot would be swamped out by heat transfer from adjacent areas.

Let's assuming that your clutch and fan are good.  Let's also assume that the water pump is good (and that it's the right one, there are 2 styles).  About all that's is a flow problem or a bad thermostat. I have seen bad thermostats and once I got a new one that was bad.  Maybe recheck that again.   Another thing I remembered - be sure that the A/C condensor is clear.  Mine was extremely clogged with bugs.  They were hard to see and harder to remove.  It seems like restricted air flow could cause your problems too.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

ramiro

Thermostats i tried 2 , also checked everyone in Boiling water and they were opening fine.

Also cleaned the A/C condensor because i had the same idea.

Last time i checked the Radiator with a ir heat gun directly after i turned the engine off and it had 100c like the cluster showed nearly all the way to the bottom , so i really doubt that i have a circulation problem.

Randys01

try a new temp sender unit.  rh head at the rear.

ramiro

why , it shows the same temp like my ir gun also the electric fan kicks on when it shows 100 so i see no reason why its reading wrong .

daantjie

This is reading more and more like head gasket but before you tear down the motor maybe get a 2nd opinion on the liquid test you performed.  I am not sure how accurate these are but likely we have to assume that since you observed colour change exhaust gasses are present in the coolant.
You can also try a compression test on all cylinders, if you see really low values on 1 or more cylinders for sure your head gasket is toast.
Daniel
1977 450 SEL 6.9 - Astralsilber

Randys01

Whilst you contemplate Daniel's reply,  we are getting mixed messages.
 In your first post you state :
The Radiator also had 100 C and ~ 85 on the Outlet so the coolant is flowing.
But then 
]Last time i checked the Radiator with an ir heat gun directly after i turned the engine off and it had 100c like the cluster showed nearly all the way to the bottom , so i really doubt that i have a circulation problem.[/quote]

Unless you have 15 degrees+- between the top of the radiator and the bottom, you do have a circulation problem.!

The reason I suggested the sender unit was simply to  eliminate it. That is after all what is causing the concern.......the gauge is reading  a 100c and from my qik reading of it all, everything else you've measured with the IR says a 100 degrees. This seems a bit too coincidental. The top radiator hose after a 180 kph fling should be > 100c. That is, there is no measured temp differential anyway you test it. Everything is 100 degrees??

Something is not right. I'd be checking the accuracy of the IR gun...the validity of the temp sender...the differential in temp between top and bottom of the radiator (there should be a discernible difference..you should almost be able to touch the bottom hose. ]
To have a reading of 100c at the temp sender unit means other parts of the cooling system should be well in excess of that.

It just doesn't seem to be running hot, .its only the temp gauge that says its 10 degrees warmer than normal. Is that a fair assessment OR ...?

ramiro

That values were after idle , after a fast drive it es exactly like you expect inlet ~110 and outlet ~ 95, temp gauge also showed 110 and everytime i meassured with a running engine its 15 degress difference, so it would be nice if the temp gauge would read high but i would it reading around +-2C precise.

Also when the engine got to 110 on the gauge it started pinging on part throttle at 160.

100 nearly all the way to the bottom was 1 minute after i turned the engine off after idling for some time the only way to check if the radiator is hot everywhere is with a non running engine because of the condenser thats why i meassured it like that.

I tried the test on 2 other cars first i got green on 1 but after cleaning the tester it stayed blue on both of them(so i am pretty sure it was contaminated still from 6.9), and after that i put it on the 6.9 again and it turned green again.

I did a compression test a year ago and 1 Cyl was down 1 bar but they were all 10 - 11 bar and the overheating is there since i first drove the car a year ago.

rumb

The leak kit you used seems to be verifying combustion gasses in the antifreeze. I read that some exhaust anylizers can dected anti freeze. Perhaps you could find a shop with such device.
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS

ramiro

I used this kit https://www.ebay.com/itm/175187507731 .

raueda1

Quote from: ramiro on 27 July 2022, 08:10 AMI used this kit https://www.ebay.com/itm/175187507731 .
based on that it does indeed look like blown head gasket.  And it makes sense. My remedies were based on the simple stuff that goes wrong most often.  Perhaps time to start searching for head gaskets but unfortunately they aren't easy to find.  You could try to classic center in California.  They used to have a whole rebuild gasket kit that was reasonably priced.  It included manifold and valve cover gasket. and many others.
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0